Select a forum to post in:

Plate Tectonics

Science topics

Moderators: Jessica, Teachers

Looking for a topic?
View the Science Topics Directory to find topics quicker under different kinds of science.

Plate Tectonics

Post Number: #1  Postby Jessica » September 23rd, 2014, 8:29 pm

In the last century we have gathered much evidence to support the idea that Earth's surface is broken up into "lithospheric" plates that slowly move over the top of the mantle. The map below shows the major plates.
Image

Plates are large pieces of the upper few hundred kilometers of Earth that move more or less as a single unit. It is easier to think of plates as rigid "rafts" floating on the mantle, but some plates also have some internal deformation. However, it is clear that the most active deformation of the plates occurs along their boundaries, where they interact with other plates.
Image

The precise thickness of a plate varies from place to place, but away from plate margins, plates are usually on the order of 100-200 km thick.

Plates are defined not on chemical differences, but using rock strength, and they are composed of the crust and the uppermost part of the mantle.

The precise lower boundary of a plate depends on the temperature of the mantle material. At about 1300°C typical mantle material begins to melt, and softens dramatically. We call that part of the mantle asthenosphere, to indicate that it is a weak zone, that "decouples" the plate from the overlying mantle (actually, there is undoubtedly some "drag" forces that act between the two, but the lithosphere can move independently of the deeper mantle.


Since the construction of the first good maps of the continents, people have puzzled over the close match between the coastlines of South America and Africa.
Image
The first to seriously investigate the connection was Alfred Wegener, a German meteorologist who proposed the continental drift hypothesis (between 1919-1929) to explain the observed shape of the coastlines and several other geologic observations regarding the observation of fossils and rocks on opposite sides of the ocean. Wegener proposed that at one time, all the present-day continents actually were combined into a "super-continent" which he called Pangaea (or Pangea).
Image


The Geomagnetic Field

The "geomagnetic" field is generated by motions of the iron in the outer core. One property of a moving conductor (such as the flowing iron in the outer core) is that it produces a magnetic field. That same magnetic field allows us to use a compass to navigate around Earth's surface. The compass needle is a small magnetic that aligns itself with Earth's magnetic "flow lines" (a magnetic field is a vector quantity, it has a direction and magnitude). In a way, compasses are instruments for measuring the direction of Earth's magnetic field.
  • 0

Tales of Ostlea : ImageImageImageImageImageImageImageImage
Dragon Cave : Image
Magistream : ImageImageImageImageImageImage
Leetle Adoptables : Image
Internetometer : Image
User avatar
Jessica
Board Owner
Topic Author

Founder
Sapphire
Sapphire
 
6 years of membership6 years of membership6 years of membership6 years of membership6 years of membership6 years of membership
 
Posts: 3,435
Topics: 1,244
Articles: 30
Joined: December 22nd, 2010, 8:04 pm
Local time: October 23rd, 2017, 8:07 pm
Last Visit: Today, 12:51 am
Location: Pennsylvania
Gender: Female
Cash on hand: 4,408.26
Bank: 125,757.08
Reputation: 148
Medals: 18
#1: July 2012 1st Place (1) R-Contest #1 First Place (1) Best staff member 2013 (1) Easter Egg Hunt 2013 (1) Graphic Drawing Participant (1) 1 Year (1) 2 Years (1) 3 Years (1) 4 Years (1) 5 Years (1)
6 Years (1) Founder (1) Highest Rep (1) Referrer (1) Top poster (1) Facebook group (1) Pin-Board (1) Article Author (1)
Referrals: 27
Blog: View Blog (449)
Subject(s): Chinese, Math
Global Moderator
Admin
Moderator

Return to Science Topics

Login  •  Register
cron
Reputation System ©'